Radiation sensors are well known in the art. One such radiation sensor is a Geiger counter which senses the emission of radiation from a radiating source and emits signals indicative of the number of charged particles impinging on a radiation sensitive crystal carried in the housing of the Geiger counter apparatus. Radiation sensors come in many different forms and are usable in many different environments.
In coal mining, for example, radiation sensors are used to detect radiation emissions from layers of shale and other materials carried in the ground. Typically, a coal mine is found to contain alternating layers of coal and shale (and other materials mixed in the shale). Radiation is generally emitted from the shale layer and through the inert coal layer. By sensing (counting) the number of charged particles striking a radiation sensor (crystal), the thickness of the coal layer can be deductively substantially determined.
In a coal mining operation, a mining machine is moved within a coal seam, and coal is extracted from the seam. The coal mining machine generally includes coal extraction apparatus which is movable in elevation while the coal mining machine is movable within the coal seam of the tunnel. Thus, the cuts must be such that while successively removing coal from the vertical surface of the coal seam, a predetermined thickness of coal is often desired to be left on the roof of the tunnel so as to prevent roof material (shale, etc.) from crashing down from above. If too much coal (roof coal) is left on the roof, much valuable and expensive coal is left in the mine, resulting in a very expensive mining operation; and, if too little roof coal is left, the layer of roof material can deteriorate, crumble, and fall, creating unsafe conditions.
In the past, one method of determining the thickness of the roof coal was to temporarily terminate the coal cutting operation and move the machine so that a drill may be used to bore through the coal layer until the coal layer was penetrated and the roof material layer contacted by the tip of the drill bit. Such procedure was time consuming and costly. Therefore, various arrangements of radiation sensing elements were resorted to in an effort to eliminate such time consuming and costly drilling procedures.